Gap junctions are found between cells of most tissues, where they provide intercellular channels that are permeable to a wide range of small hydrophilic molecules. In the heart and nervous system, gap junctions allow rapid and faithful transmission of electrical current that is carried by junction permeant ions. The function of gap junctions in other tissues is not as clear, and analysis of physiological roles is complicated by the recent discovery that gap junction proteins are encoded by a family of genes and that various gap junction channels have different properties. Project I seeks to correlate properties of gap junctions with the junctional proteins and to extend our understanding of the role of gap junction channels in several tissues where previous work has been incomplete. For selected tissues (endothelial cells, smooth muscle from myometrium and vascular beds, skin (keratinocytes), pancreatic islet, melanocytes and retinal pigment epithelium, and lens fibers) effects of hormones and other agents on junctional conductance will be chosen for their relevance to normal and altered physiological functions. Nevertheless, the goals of these studies are similar: to determine the identity of tissue-specific connexins using biochemical and immunological techniques to identify the proteins and in situ hybridization and Northern blot analysis to identify the mRNAs. For each tissue, electrophysiological techniques will be used to identify single channel and macroscopic conductances of channels that correspond to the connexins. Electrophysiological studies will analyze mechanisms of regulation of junctional conductance in each system, and together with studies of second messenger effects on protein phosphorylation should indicate the potential flexibility in intercellular signaling through these channels as a consequence of this covalent modification. Physiological and pharmacological studies will determine classes of agents that affect intercellular communication and will compare response of cells containing identified connexins. By examining whether junctional conductance is regulated under conditions of physiological stimulation and pathological insult, we hope to gain further insight into the roles that gap junctions play in normal and diseased tissue.